AM79C930VCW datasheet(116/161 Pages) AMD

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P R E L I M I N A R Y

116

Am79C930

edge baud counter. This information should be used to appropri-

ately program the Baud Detect Upper Limit register.

The resolution of the value in this register is the period of the CLKIN

signal when the CLKGT20 bit of MIR9 is set to 0 or twice the period

of the CLKIN signal when the CLKGT20 bit of MIR9 is set to 1. With

CLKIN = 20 MHz and CLKGT20=0, a value of 14h (=20 decimal)

represents the

nominal like transition separation value for a 1Mbit/s

network data rate.

TCR19: Baud Detect Accept Count for Carrier Sense

This register is the Baud Detect Accept Count for Carrier

Sense register. When the number of positive baud de-

tect test results in the baud detection circuit reaches the

value in this register, then the total number of tests taken

to that point will be considered adequate to make a valid

determination of positive carrier sense. The number of

positive baud detect test results is reset to 0 each time

that the antenna selection is changed.

CONFIGURATION REGISTER INDEX:

13h

Bit

Name

Reset Value

Description

7–6

Reserved

–

Reserved. Must be written as a 0. Reads of this bit produce

undefined data.

5–0

BDCS[5:0]

00h

Baud Detect accept count for Carrier Sense. When the number of

positive baud detect test results in the baud detection circuit

reaches the value in this register, then the total number of tests

taken to that point will be considered adequate to make a valid de-

termination of positive carrier sense. The number of positive baud

detect test results is reset to 0 each time that the antenna selection

is changed.

TCR20: Baud Detect Accept Count for Stop Diversity

This register is the Baud Detect Accept Count for Stop

Diversity register. When the number of positive baud de-

tect test results in the baud detection circuit reaches the

value in this register, then the total number of tests taken

to that point will be considered adequate to make a valid

determination of satisfactory antenna selection. The

number of positive baud detect test results is reset to 0

each time that the antenna selection is changed.

CONFIGURATION REGISTER INDEX:

14h

Bit

Name

Reset Value

Description

7–6

Reserved

–

Reserved. Must be written as a 0. Reads of this bit produce unde-

fined data.

5–0

BDSD[5:0]

00h

Baud Detect accept count for Stop Diversity. When the number of

positive baud detect test results in the baud detection circuit

reaches the value in this register, then the total number of tests

taken to that point will be considered adequate to make a valid de-

termination of satisfactory antenna selection. The number of posi-

tive baud detect test results is reset to 0 each time that the antenna

selection is changed.

TCR21: Baud Detect Ratio

This register is the Baud Detect Ratio register. This reg-

ister is used to set the ratio of good to bad baud detec-

tions which will be used as the minimum ratio to

determine that a valid signal is present on the medium.

The value in this register is treated as a radix 2 positive

real number with two decimal places. The lowest practi-

cal value possible is 0.25 (=00.01) and the highest prac-

tical value is 3.75 (=11.11).

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